The demand for high performance in bipolar transistors requires a copper interconnect to carry high current density and also work at high temperatures. This places severe challenges on copper interconnect reliability, especially concerning electromigration issues. Electromigration decreases the reliability of integrated circuits (ICs), with eventual loss of connections or failure of the circuit. Also, with increasing miniaturization, the probability of failure due to electromigration increases in very-large-scale integration (VLSI) and ultra-large-scale integration (ULSI) circuits because both the power density and the current density increase. Thus, as the structure size in ICs decreases, the practical significance of the electromigration effect increases.
In advanced semiconductor manufacturing processes, copper has replaced aluminum as the interconnect material of choice. Despite its greater fragility in the fabrication process, copper is intrinsically less susceptible to electromigration. However, electromigration continues to be an ever present challenge to device fabrication.
Some research has lead to simply widening metal lines in order to address electromigration issues. However, this is not satisfactory, particularly for VSLI and ULSI circuits. For example, increasing metal line width can only increase the current carrying capability, linearly, while the high junction temperature degrades the current carrying capability exponentially. Furthermore, using metal lines much wider than the device contact will have current crowding issues and device density issues. Also, a high temperature gradient along the interconnect can cause thermal migration and stress migration problems.
Accordingly, there exists a need in the art to overcome the deficiencies and limitations described hereinabove.